No-can no-fill mechanism for filling machines



Jan. 13, 1970 L. c. RIKER 3,489,186

NO-CAN NO-FILL MECHANISM FOR FILLING MACHINES Filed June 9, 19672'SheetsSheet l INVENTOR LAWRENCE C. RIKER ATTORNEY Jan. 13, 1970 L. c.RIKER 3,489,136

NO-CAN NO-FILL MECHANISM FOR FILLINGMACHINES Filed June 9, 1967 2Sheets-Sheet 2 e6 88 so 2 g 80 -84 92 am 82 se FIG. 4

LL fl 78 78 "W%f {||l -'W v {l|l FIG. 5 FIG. 6

INVENTOR LAWRENCE C. RIKER ATTORNEY United States Patent York Filed June9, 1967, Ser. No. 644,971 Int. Cl. B65b 57/06; B266 5/28 US. Cl. 141-1416 Claims ABSTRACT OF THE DISCLOSURE In a no-can no-fill mechanism forrotary filling machines having a plurality of filling stations, a pairof limit switches wired in parallel and two trip shoes for activatingthe mechanism whenever a filling station is not occupied by a containerto be filled. The mechanism remains inactive only when both trip shoesare depressed by engagement with containers occupying the fillingstations and releasing either trip shoe, activates the no-can no-fillmechanism to prevent filling at an unoccupied station. The trip shoesare overlapped and slightly offset from one another, so that the last ofa series of containers will pass off and release the first shoe whilestill holding the second depressed.

The present invention relates to a filling machine for filling cans,glass jars or other containers with various free flowing liquids orsemi-flowing products, and more particularly to a mechanism for use inconnection with such machines for maintaining the filling mechanism inoperative when no container is in a position to be filled.

Reference is made to the patent of Joseph T. Stigler, No. 2,759,649 andthe patents referred to therein which show a typical prior art no-canno-fill mechanism and a typical filling machine to which the presentinvention can be applied. For purposes of providing background for thepresent invention, the operation of a typical filling machine on whichthe present invention can be used and a typical prior art no-can no-fillmechanism is only generally described since the details thereof aredescribed in the patents referred to above. It should be understood thatthe no-can no-flll mechanism of the present invention may beincorporated in any machine of the general type described in the abovecited patents or similar rotary container handling machines.

Such a filling machine includes a plurality of filling stations equallyspaced about the periphery of a rotating turret. Associated with eachfilling station is a valve which opens and closes to permit the fillingof containers which occupy the filling stations. Opening and closing fthe filling valves is controlled by a cam follower carried by each ofthe filling valves, the follower being deflected in one direction toopen the valve and in the opposite direction to close the valve. The camfollower is deflected to Open the valve by a cam which is movable intoand out of the path of travel of the cam followers. If the cam is in thepath of travel, the follower will be deflected to open the valve. On theother hand, if the cam is moved from the path of travel, the followerwill not be deflected and the valve will remain closed. As long as eachfilling station is occupied by a container to be filled, the cam willremain in the path of the cam follower. However, if for some reason oneor more filling stations are not occupied by containers, the cam ismoved from the path of the cam followers to prevent the opening of thefilling valves associated with the unoccupied stations.

The cam is moved by any suitable drive means such as a solenoid, an aircylinder or the like, which is energized by closing a switch. In theprior art this switch is Patented Jan. 13, 1970 ice opened and closed bya single trip shoe resiliently mounted in a position which lies normallyin the path of travel of the containers. Upon contact with thecontainers occupying the filling stations, the trip shoe is moved to adepressed position which opens the switch. Therefore, as long as theshoe is depressed by a container, the solenoid is de-energized so thatthe cam remains in the path of travel of the cam followers. However, ifa filling station is unoccupied, the trip shoe will move to its normalposition in the path of travel of the containers closing the switch.Closing the switch in turn energizes the solenoid and removes the camfrom the path of the cam followers.

To prevent unnecessary movement of the trip shoe, the length of the shoeis made substantially equal to the center-to-center distance of thefilling stations to allow a steady stream of containers to hold the tripshoe in the depressed position without fluttering. Thus, the trip sh ein the prior art only moves in two situations, when an unoccupiedfilling station is followed by an occupied filling station, or when anoccupied filling station is followed by an unoccupied filling station.The first situation is termed a no-can to can condition and the secondsituation is termed a can to no-can condition.

Furthermore, since the single trip shoe of the prior art is equal inlength to the center-to-center distance between filling stations, thecontainer following an unoccupied station in the no-can to can conditioncontacts and depresses the trip shoe before the center line of theunoccupied station has completely traversed the trip shoe. Thus, in theno-can to can condition, the cam is advanced into the path of the camfollowers when the container moves the trip shoe to the depressedposition, which occurs before the unoccupied station has completelytraversed the trip shoe. However, in the can to no-can condition, thecam is retracted from the path of the cam followers when the trip shoehas moved to its normal position. This occurs after the containerpreceding an unoccupied filling station has completely traversed thetrip shoe or when the center line of the unoccupied station is locatedat some point on the trip shoe. Accordingly, with a single trip shoe thecam follower representing an unoccupied filling station is closer to thecam when the cam is retracted than the cam follower representing anoccupied filling station is to the cam when the cam is advanced.

While this distance differential does not influence the low speedoperation of the filling machine, it becomes an important factor whenthe filling machine is operated at high speeds, and, in fact, limits thetop speed of the filling machine.

For example, experiments conducted on a 35 station rotary fillingmachine operating at a speed of 1,000 containers per minute show thatthe cam followers passed a fixed point every .0600 second. Of this time,.0327 second was required for the cam follower to traverse the length ofthe cam surface and an additional .0065 second was required for thefollower to clear the cam. The remaining .0208 second of the total cyclerepresented the time available for moving the cam. In the no-can to cancondition, it was found that the cam was advanced into the path of a camfollower when the follower was still the full .0208 second away from thecam. However, in the can to no-can condition, the cam was retracted fromthe path of a cam follower when the follower was only .0035 second awayfrom the cam. Because of the relatively short time available forretracting the cam from the path of the cam followers, it was foundempirically that the actual safe reliable operational speed of thefilling machine was in the neighborhood of 800 cans per minute ratherthan a top speed of 1,000 cans per minute, the speed of the machinebeing reduced to provide sufiicient time for retracting the cam from thepath of the cam followers.

3 SUMMARY OF INVENTION In the preferred embodiment of the presentinvention, the single trip shoe of the prior art is replaced by two tripshoes, one shoe to control the advance of the cam into the path of thecam followers and another trip shoe to control the retraction of thecam. Each trip shoe is operatively connected to a switch, the twoswitches being connected in parallel to a solenoid. With thisarrangement, the solenoid is energized and the cam retracted when eithertrip shoe is in its normal position. In like respect, the solenoid isde-energized and the cam advanced only when both trip shoes are in adepressed position.

In experiments conducted on the same 35 station filling machine usingtwo trip shoes, it was found that the reaction time of the no-canno-fill mechanism was increased so that the cam could be retracted fromthe path of a cam follower associated with an unoccupied filling stationwhile the cam follower was still the full .0208 second away from thecam. Thus, with the two strip shoe arrangement, it was found the safereliable speed for continuous operation of the 35 station fillingmachine was increased to 1,000 containers per minute, an increaserepresenting at 25% improvement in the production rate of this machine.

OBJECTS OF THE INVENTION One object of my invention is to provide animproved triggering device for activating no-can no-fill mechanisms.

Another object of my invention is to provide a sensing and triggeringdevice for activating a no-can no-fill mechanism which utilizes at leasttwo trip shoes to indicate the presence or absence of containers atfilling stations.

A further object of my invention is to provide a sensing and triggeringdevice for no-can no-fill mechanisms which increase the safe, reliableoperating speed of filling ma- :hines.

A still further object of my invention is to provide a no-can no-fillmechanism which utilizes the maximum amount of time available to bothadvance and retract the valve opening cam from the path of the fillingvalve.

These and other objects, advantages and characterizing Eeatures of myinvention will become more apparent upon consideration of the followingdetailed description thereof when taken in conjunction with theaccompanying drawings depicting the same.

DESCRIPTION OF DRAWINGS FIGURE 1 is a schematic representation of theno-can 1o-fill mechanism of my invention showing a double trip shoearrangement for indicating the presence or absence 3f containers atfilling stations.

FIGURE 2 is a view taken along line 22 of FIG- URE 1.

FIGURE 3 is a view taken along line 33 of FIG- URE 1.

FIGURE 4 is a view similar to FIGURE 3, only showng another embodimentof my invention which utilizes :hree trip shoes.

FIGURE 5 is an electrical schematic of the switches associated with thetrip shoes shown in FIGURE 4.

FIGURE 6 is a view similar to FIGURE 5, showing a ichernatic of stillanother embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, theno-can .no-fill mechanism )f my invention is preferably used on afilling machine which is circular in plan. The general construction of anachine on which the no-can no-fill mechanism of my inlention isincorporated will not be described in detail, IIHCE the details thereofare described in the Stigler Patent Io. 2,759,649, referred to above andthe references cited :herein. For purposes of clarifying the presentinvention, have shown schematically in FIGURE 1 a portion of therotating turret indicated at 12 of the filling machine and one of themultiplicity of cylinders indicated at 14. Mounted below each of thecylinders 14 is a valve body 16 in which a conical valve 18 is seated.The valve 18 has an arm 20 rigid therewith upon the end of which aroller 22 is mounted. It will be understood that the valve has a fillingport 26 which is movable into either of two positions. One positionprovides a filling opening between the cylinder and the containers to befilled and the other position closes off communication from thecylinder.

All of the above mechanisms are completely described in the abovementioned patents. With respect to the valve construction, it issufficient to state that special connecting ports are provided but thatfor the purpose of this application all that is required is that thevalve be opened in one position and closed in the other position.

Also shown in FIGURE 1 is a container 30 representing the multiplicityof containers that are carried on the rotating turret 12, at fillingstations located beneath cylinders 14 so that when valve 18 is opened,product within the cylinder can be fed into the container locatedtherebeneath.

Mounted in the path of travel of rollers 22 is a valve opening cam 42,which, as long as containers are supplied to the machine, does not movefrom the position shown in solid line in FIGURE 1. Thus, cam 42 isnormally always in a position to engage rollers 22 to rotate valve 18 ina counterclockwise direction (FIGURE 2) to enable the containers to fillwith material being discharged from cylinders 14.

The containers are filled as they rotate with turret 12. When thecontainers are filled, rollers 22 engage a stationary valve closing cam(not shown) which rotates the rollers in a clockwise direction to closevalves 18.

Referring now to FIGURES 1 and 3, carried by any suitable fixed part ofthe machine is a pivot 44 upon which arms 46 and 48 are pivotallymounted. Springs 50, having one end mounted on a fixed part of themachine and another end attached to arms 46 and 48, normally urge thearms in a clockwise direction about pivot 44 as viewed in FIGURE 1. Eacharm 46, 48 carries remote from springs 50 a trip shoe 60, 62respectively. Each trip shoe 60 and 62 has a container engaging portion64, 66 substantially equal in length to the center-to-center distancebetween filling stations. Container engaging portions 64, 66 normallylie in a position in the path of travel of the containers as shown inphantom in FIGURE 3, but are moved to the position shown in solid lineupon engagement with the containers. FIGURES 1 and 3 also show that tripshoes 60 and 62 are disposed one above the other (FIGURE 1) and areoffset one from the other in the direction of container travel (FIGURE2) to form offset end sections and 72 and an overlapped intermediatesection 68. It will be appreciated that intermediate section 68 has acontainer engaging portion of a length less than the distance betweencontainers, but that the intermediate section 68 together with eitherend sections 70 or 72 define a container engaging portion which issubstantially equal to the center-to-center distance of the containers.Moreover, both trip shoes together define a container engaging portion(68+70+72) which is greater than the center-to-center distance of thecontainers.

Associated with each arm 46 and 48 is a limit or snap action switch 74and 76 respectively. Switches of this character are well known and neednot be described in detail. It should be suificient for purposes ofunderstanding the present invention to say that when either containerengaging portion 64 or 66 is in the position shown in phantom in FIGURE3 the switch associated with the arm carrying that portion is closed. Asshown in FIGURE 1, switches 74, 76 are connected in parallel to asolenoid 78, which in turn is operatively connected to valve opening cam42. Thus, closing either switch 74 or 76 will energize solenoid 78 tomove cam 42 out of the path of travel of cam followers to the positionshown in dotted line in FIGURE 1.

To describe the method of operation of the no-can nofill mechanism of myinvention and by way of illustration only, I shall describe theoperation as beginning with all filling stations on rotating turret 12unoccupied. In this situation container engaging portions 64, 66 are inthe position represented in phantom in FIGURE 3. With trip shoes 60, 62and their respective container engaging portions in this position,switches 74, 76 are both closed, solenoid 78 is energized, cam 42 is inthe position shown in dotted line in FIGURE 1 and filling valves 18remain closed as turret 12 rotates. Assume now that the first container30 enters a filling station on rotating turret 12 and moves in thedirection indicated by arrow 81 in FIGURE 3. Container 30 first engagestrip shoe 62, moving this trip shoe to the position indicated in solidline in FIGURE 3, but trip shoe 60, however, remains in the positionindicated in phantom in FIGURE 3. As viewed in FIGURE 1, the engagementbetween container 30 and trip shoe 62 moves the trip shoecounterclockwise opening switch 76. However, since the container has notyet engaged trip shoe 60, switch 74 is still closed so that the solenoidremains energized to keep cam 42 out of the path of travel of camfollower 22. As container 30 continues in its path of travel it willnext engage trip shoe 60 moving this trip shoe to the position indicatedin solid line in FIGURE 3. As viewed in FIGURE 1, this engagement movestrip shoe 60 and arm 46 counterclockwise so that switch 74 is opened.Now, with both switches opened, solenoid 78 is de-energized, allowingcam 42 to move into the path of travel of cam follower 22 under theinfluence of any suitable means such as spring 41. With the cam in thisposition, the follower 22 associated with the filling station occupiedby container 30 is moved counterclockwise to open valve 18. I

Since the container engaging portion 64 and 66 of each trip shoe isequal to the center-to-center distance between filling stations, it willbe appreciated that the next container 32 (FIGURE 3) occupying the nextsuccessive filling station, will be in a position to depress trip shoe62 just as the center line of container 30 passes off of the shoe. Also,by the time container 30 has completely passed off trip shoe 60, thenext following container 32 will be located in the intermediate section68, holding both trip shoes in a depressed condition. Therefore, as longas a continuous stream of containers is supplied to the machine, bothtrip shoes will remain in a depressed condition holding both switches74, 76 open. With both switches open, solenoid 78 is de-energized,allowing cam 42 to remain in the path of travel of the filling valvesand cam followers 22.

Assume now that the next filling station in sequence is unoccupied, anabsent container 34 being represented in dotted line in FIGURE 3. Sincecontainer 34 is not present on the machine, trip shoe 62 will move tothe position indicated in phantom in FIGURE 3 when container 32 hastraversed both end section 70 and intermediate section 68 and is locatedin section 72. Since there is no container present to hold trip shoe 62depressed, it will move to its normal position in the path of travel ofthe containers as indicated in phantom. As viewed in FIGURE 1, thismovement rotates trip shoe 62 and arm 48 clockwise causing switch 76 toclose. Since switches 74 and 76 are wired in parallel, closing eitherswitch will activate solenoid 78 and withdraw cam 42 from the path ofthe filling valves and cam follower 22. The cam remains in the positionindicated in dotted line in FIGURE 1 until both trip shoes are againmoved to a depressed position.

Therefore, with the double trip shoe arrangement, the cam is not movedinto the path of travel of the cam followers until both the trip shoesare depressed, which situation occurs when a container has moved ontothe intermediate portion 68. However, the solenoid is activated toremove the cam from the path of the filling valves whenever either tripshoe is returned to its normal position in the path of travel of thefilling stations. This may occur,

for example, while the last container of a series of containers is stillpresent at end section 72 holding trip shoe 60 in 'a depressed position.

Thus, it should be appreciated that in the no-can to can condition, thesolenoid is not de-energized until the first of a series of containershas engaged and moved trip shoe 60 to a depressed position and in a canto no-can condition, the solenoid is energized when the last of a seriesof containers has passed off of trip shoe 62, but is still holding tripshoe 60 in a depressed position. Thus, in relation to the operation ofthe single trip shoe of the prior art, it will be appreciated that thepresent invention, in the no-can to can condition, would de-energize thesolenoid at substantially the same time as a single trip shoe. However,during the critical can to no-can condition, the double trip shoe of thepresent invention would energize the solenoid before the single tripshoe of the prior art could operate.

While the double trip shoe arrangement represents the preferredembodiment of the invention, there are other embodiments which wouldoperate equally as well; for example, in the embodiment shown in FIGURE4, three trip shoes 80, 82 and 84 are used. Each trip shoe 80, 82 and 84carries a container engaging portion 86, 88 and 90 respectively, whichlie in a normal position in the path of travel of the containers. Thelength of each container engaging portion is such that the length of theintermediate portion 88 together with either portion 86 or 90 defines alength substantially equal to the center-tocenter distance of thefilling station. Upon engagement with a container, the trip shoes aremoved to a depressed position actuating switches 92, 94 and 96. As seenin the schematic of FIGURE 5, the switches 92 and 96 associated with endtrip shoes 80 and 84 respectively are connected in parallel and switch94 associated with intermediate trip shoe 82 is connected in series withthe parallel connected switches 92 and 96. With this arrangement,solenoids 78 is energized only when switch 94 and either switch 92 or 96is closed. This situation occurs only when immediate trip shoe 82 and atleast one of the end trip shoes is in a normal position.

In FIGURE 6 is represented a schematic of still another embodiment ofthe invention. Here the solenoid is normally energized to maintain thecam in the path of travel of the cam followers, and is de-energized toremove the cam from the path of travel of the cam followers. In such asituation, the switches 100 and 104 associated with the end trip shoeswould be connected in series and the switch 102 associated with theintermediate trip shoe would be connected in parallel with the seriesconnected switches. With this arrangement, the solenoid would bede-energized for moving the cam from the path of travel of the fillingstations only when the intermediate trip shoe and at least one of theend trip shoes are in a normal position. However, since this embodimentrequires that the solenoid be energized for a long period of time tomaintain the cam in the path 'of travel of the cam followers, it is nota preferred embodiment. It is preferred for longer life of the solenoidto energize the solenoid only in instances when a container is notsupplied to the filling machine.

Thus, it will be appreciated that the present invention accomplishes itsintended objects providing a no-can nofill mechanism which respondsquickly to the absence of containers from filling stations to preventthe opening of filling valves associated with these unoccupied stations.

While I have described the preferred embodiments of my invention asrepresenting an improvement in no-can no-fill mechanisms it should bereadily apparent to one skilled in the art that the mechanism'of myinvention can be readily adapted to other applications. For example, themechanism of the present invention is equally applicable to artsassociated with filling such as washing, painting or coating containersprior to filling or the capping and labeling of containers subsequent tofilling. Moreover,

he present invention is equally applicable not only to fillng machinesand the like but also to any situations wheren a continuous stream ofsubstantially equally spaced vorkpieces are moved linearly or arcuatelythrough a vork station where operations such as painting, sandlasting,cleaning, boring, drilling, tapping, threading, =tc., are performed onthe workpiece. The present invenion can be utilized to suspend suchoperation at the work :tation whenever one or more workpieces are absentfrom he continous stream. In this respect while I have decribed thefigures as being schematic representations of t no-can no-fill mechanismit should be readily apparent hat the reference numerals 30, 32 and 34can represent any article or workpiece other than containers and that hereference numeral 14 can represent any work station )ther than a fillingcylinder.

Having described my invention in detail what I claim lS new is:

1. In an apparatus for continuously moving a steady dream ofsubstantially equally spaced workpieces through I. path of travel, atleast one device located adjacent said )ath of travel for performing anoperation on the work- )ieces moving through said path of travel, meansfor sus- )ending the operations performed by said device when 1workpiece is absent from said steady stream comprising:

(a) trip-shoe means having aligned intermediate and end portions, saidtrip shoes means being of a length greater than the distance betweensuccessive workpieces and said intermediate portion being of a lengthless than the distance between successive workpieces;

(b) means for resiliently maintaining said intermediate and end portionsin a normal position in the path of travel of said workpieces, saidportions movable to a depressed position upon being engaged byworkpieces moving through said path of travel;

(c) drive means operatively connected to said device and activated bysaid trip shoe means for rendering said device inoperative andsuspending the operations performed by said device when saidintermediate and at least one of said end portions are in said normalposition; and

(d) a switch associated with and actuated by each of said alignedintermediate and end portions for energizing said drive means when saidportions are engaged by said work pieces and moved to said depressedposition,

(i) said switches associated with and actuated by said end portionsbeing connected in parallel with said drive means, and

(ii) said switch associated with and actuated by said intermediateportion being connected in series with said parallel connected switches,

vhereby said drive means is activated for rendering said leviceinoperable when said intermediate portion and at least one of said endportions are in said normal )osition.

2. A no-can no-fill mechanism for container filling ma- :hines whichinclude a plurality of filling valves, said illing valves being movableinto either a closed position )r an open position, means for supplyingcontainers to )e filled beneath each of said filling valves, means fornoving said filling valves and containers through a path )f travel andvalve opening means for moving said filling Ialves to said openposition, said no-can no-fill mechanism :omprising:

(a) at least two aligned trip shoes which together provide a containerengaging portion of the length greater than the distance betweensuccessive containers, each of said trip shoes being of a lengthsubstantially equal to the distance between successive containers, eachof said trip shoes being resiliently maintained in normal position inthe path of travel of said containers and movable to a depressedposition upon being engaged by containers moving through said path oftravel; and

(b) means actuated by said trip shoes for rendering said valve openingmeans inoperative when at least one of said trip shoes are in saidnormal position.

3. A no-can no-fill mechanism as set forth in claim 2 in which said tripshoes comprise:

(a) a first trip shoe; and

(b) a second trip shoe overlapping said first trip shoe and oifsettherefrom in the direction of container travel to define an overlappedsection and offset end sections, wherein'a container engaging one ofsaid offset end sections will depress one of said trip shoes and acontainer engaging said overlapped section will depress both of saidtrip shoes.

4. A no-can no fi-ll mechanism as set forth in claim 3 in which saidmeans actuated by said trip shoes comprises:

(a) drive means operatively connected to said valve opening means formoving said valve opening means to an inoperable position;

(b) a first switch actuated by said first trip shoe for energizing saiddrive means;

(0) a second switch actuated by said second trip shoe for energizingsaid drive means connected in parallel with said first switch; and

((1) said first and second switches being closed when said trip shoesare in said normal position and opened when said trip shoes are in saiddepressed position, whereby said drive means is energized for movingsaid valve opening means to an inoperable position when either of saidtrip shoes is in said normal position.

5. A no-can nO-fill mechanism for container filling machines whichinclude a plurality of filling valves, said filling valves being movableinto either a closed position or an open position, means for supplyingcontainers to be filled beneath each of said filling valves, means formoving said filling valves, and containers through a path of travel andvalve opening means for moving said filling valves to saidopen-position, said no-can no-fill mechanism comprising:

(a) trip shoe means including a pair of aligned trip shoes overlappedand offset one from the other in the direction of the'container travel,each of said trip shoes having a container engaging portionsubstantially equal tothe center-to-center distance of successive onesof said containers;

(b) means for resiliently maintaining said trip shoes in a normalposition in the path of travel of said containers, said trip shoesmovable to a depressed position upon being engaged by containers movingthrough said path of travel;

(c) drive means operatively connected to said valve opening means forrendering said valve opening means inoperative; and

((1) means for actuating said drive means including at least twoparallel connected switches, one of said parallel connected switchesbeing associated with and operated by each of said trip shoes, wherebymovement of either trip shoes to said normal position will actuate saiddrive means.

6. In an apparatus for continuously moving a steady stream ofsubstantially equally spaced workpieces through a path of travel and atleast one device located adjacent said path of travel for performing anoperation on the workpieces moving through said path of travel, meansfor suspending the operations performed by said device when a workpieceis absent from said steady stream comprising:

(a) trip-shoe means having aligned intermediate and end portions, saidtrip-shoe means being of a length greater than a distance betweensuccessive workpieces and said intermediate portion being of a lengthless than the distance between successive workpieces;

(b) means for resiliently maintaining said intermediate and end portionsin a normal position in the path of travel of said workpieces, saidportions movable to a depressed position upon being engaged byworkpieces moving through said path of travel;

(0) drive means operatively connected to said device and activated bysaid trip-shoe means for rendering said device inoperative andsuspending the operations performed by said device when saidintermediate and at least one of said end portions are in said normalposition; and

(d) a switch associated with and actuated by each of said alignedintermediate and end portions for energizing said drive means when saidportions are engaged by said workpieces and moved to said depressedposition,

(i) said switches associated with and actuated by said end portionsbeing connected in series with said drive means, and

(ii) said switch associated with and actuated by said intermediateportion being connected in parallel with said series connected switches,

whereby said drive means is energized to render said valve opening meansoperative when said intermediate portion and at least one of said endportions are in said normal position.

References Cited UNITED STATES PATENTS 10 2,759,649 8/1956 Stigler141-143 FOREIGN PATENTS 563,262 9/1958 Canada.

U.S. Cl. X.R.

